The results unveiled Wednesday could reinforce Abbott's position as a key player in an industry race to bring the next generation of drugs to what is expected to be a multibillion-dollar market for hepatitis C therapies. The drugs' safety and efficacy, however, need to be confirmed in additional studies.

"The Abbott data are clearly impressive from an efficacy perspective," said ISI Group analyst Mark Schoenebaum.

Abbott shares rose 46 cents, or 0.7%, to $61.58 in recent trading, and earlier set a 52-week high of $62.57.

Abbott has said it could begin selling a new hepatitis C regimen in 2015, and sales could eventually exceed $2 billion annually. The drugs would be sold by the pharmaceutical business that Abbott plans to split off into an independent company later this year, to be named AbbVie.

Summaries of the Abbott studies and studies of other liver-disease drugs were posted online Wednesday by the European Association for the Study of the Liver, or EASL, in advance of its annual scientific meeting in Barcelona in mid-April. Some EASL study summaries won't be released until the conference begins.

Hepatitis C is a viral disease that attacks the liver, and is believed to afflict about 180 million world-wide, with more than 4 million in the U.S., according to the National Institute of Allergy and Infectious Diseases. At-risk groups include people who had blood transfusions before 1992, when a screening test for the virus was developed.

Abbott is developing several potential hepatitis C drugs. One of them, ABT-450, is a so-called protease inhibitor, which is the same class of drugs as two that went on sale last year, Merck's Victrelis and Vertex's (>> Vertex Pharmaceuticals Incorporated) Incivek, which is marketed outside the U.S. by Johnson & Johnson (>> Johnson & Johnson) as Incivo.

The protease inhibitors advanced treatment of hepatitis C, but there is still room for improvement because current treatments require an injectable drug, interferon, that can be difficult for patients to tolerate. Abbott and other companies want to develop all-oral regimens that eliminate the need for interferon.

In addition, Abbott is developing two polymerase inhibitors, ABT-072 and ABT-333, which have different mechanisms of action than the protease inhibitors.

The two studies released Wednesday each focused on ABT-450. One, titled "Co-Pilot," involved 50 patients who were given the following: one of two different dose levels of ABT-450, combined in the same pill with Abbott's Norvir boosting agent; ABT-333; and an existing drug called ribavirin that is part of the current standard of care for hepatitis C. The regimen amounted to several pills taken daily.

The study tested safety and tolerability of a 12-week regimen of the drugs in people with the most common form of hepatitis C, known as genotype 1. Patients in the study either hadn't previously received any treatment or didn't respond to prior treatment.

In the treatment-naive patient groups, more than 90% had a sustained virologic response 12 weeks after the end of treatment, a measure known as SVR12. Sustained virologic response is roughly equivalent to being virus-free or having nearly undetectable viral levels.

In the patients who didn't respond to prior treatment, 47% achieved SVR12 in the Abbott-funded study.

The second, smaller study--called "Pilot"--combined ABT-450 boosted by Norvir, ribavirin, and ABT-072. All 11 patients had received no prior therapy. This group of patients had a subtype of the virus that generally responds well to an interferon-based regimen and thus considered among the easier forms to treat.

Ten of the 11 patients achieved a sustained virologic response 24 weeks after stopping treatment, for an SVR24 rate of 91%. One patient relapsed.

"We're showing a sustained, post-treatment response from 12 to 24 weeks out" from the end of treatment, said Scott Brun, divisional vice president of infectious disease development at Abbott.

In both studies, the most common adverse events included headache, fatigue and nausea, and most were mild. In the larger "Co-Pilot" study, four patients had severe adverse events including fatigue and vomiting. There were no deaths in either study.

Abbott is conducting large mid-stage studies testing various combinations of the three experimental drugs used in the smaller studies, Brun said. Abbott hopes to move some combination of the drugs into late-stage testing next year.

Abbott developed ABT-450 in collaboration with Enanta Pharmaceuticals.

Shares of some of Abbott's rivals in the hepatitis C field declined Wednesday. Idenix Pharmaceuticals Inc. (IDIX) dropped 6% to $9.62; Gilead was off 3% at $46.57; while Vertex and Bristol-Myers were each down less than 1%.